Astra's Almanac

April 2012 - Vol. 16, No. 4

This Month's Night Sky - NOTE: The next paragraph describes the sky as it
appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks
this way at 11 pm EST (midnight EDT) during the beginning of the month and
at 9 pm EST (10 pm EDT) by month's end.

Angular Measurement Review: It is interesting to note that the relationship between the angle subtended by combinations of fingers on your fully outstretched arm are the same for all viewers. This is due to the fact that the hand's size is proportional to the arm's length. A shorter arm is attached to a smaller hand while a longer arm is attached to a larger hand, thus the angle measured remains the same. If you hold your arm fully outstretched, your little finger, when sighted down your arm, is one degree wide. Your three middle fingers is five degrees, your fist, 10 degrees, and the distance between your little finger and your pointer finger is 15 degrees no matter what your age or size.

April brings the lengthening days as the Sun returns to the northern side of planet Earth. The constellation of the lion, Leo is riding high and the Virgo cluster of galaxies, discussed in last month's issue are still with us, but fade fast as the height of Spring arrives so observe as soon as the full moon fades. The first few months of the year have provided observer;s many clear nights during an unusually warm winter. The winter constellations of Orion and Canis Major set earlier in the evening, destined to disappear from the evening sky until Winter returns to the northern hemisphere.

MERCURY appears in the morning skies this month peaking over the horizon on the first and rising until it reaches greatest elongation on the 18th. This apparition favors the southern hemisphere, so take care when looking toward the Sun. VENUS is now past greatest elongation, but will continue to brighten until it reaches -4.7 magnitude later in the month. The fantastic dance of Jupiter and Venus comes to a close as JUPITER plunges into the western horizon, heading toward conjunction behind the Sun. The Venus/Jupiter pairing we've enjoyed in 2012 will not be repeated again for 35 years! MARS just past opposition, still offers visual observers the chance to see some more planetary antics in the celestial dance. Watch the red planet this month as it nears the first magnitude star, Regulus in the constellation Leo, the subject of this month's almanac. SATURN rises in the late evening, following Mars and moving toward opposition next month. The ringed planet joins the red planet this year as as the planetary dance continues, keep a sharp eye on the sky as these two planets will meet each other in August, separated by less than 5 degrees.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time; dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times. Unfortunately some of these events may occur during daylight hours in your area.

DATE

EVENT

01

Mars and Regulus within 6 deg as the month opens. Keep your eye on these two!

02-03

Venus dances with the seven sisters of the Pleiades, spectacular to watch in binoculars.

05

First magnitude star Spica and Saturn meet up in Virgo.

06

Spica and Saturn are joined by the Full Moon.

6-9

The Moon at perigee this month brings some of the highest Spring tides to the coastal areas

14

Venus within a degree of the Pleiades

15

Saturn at Opposition. The ringed planet at closest approach is still 8.7 AU away from Earth. The rings are tilted 32 degs toward the Earth, providing an excellent view in a small telescope.

17

Venus 10 degrees N of Aldeberan.

18

Mercury at greatest elongation, morning sky.

21-22

Lyrids Meteor Shower occurs this year during the new Moon. The average rate for this shower is about 10-20 meteors per hour at peak, but the Lyrids have occasionally surprised observers with rates up to 100 per hour. As an extra added bonus, the peak night of the shower, April 21, is a Saturday night.

22

Jupiter 2 degrees S of the Moon.

25

Venus 6 degrees N of Moon.

28

Astronomy Day is celebrated by local astronomical societies, planetariums, museums, and observatories that sponsor observing sessions, presentations, and other activities intended to increase public awareness about astronomy and the universe. Events are coordinated by the Astronomical League- - so click on the link to find out more and discover an event near you.

30

Venus' greatest illumination extent or greatest brilliancy. Look for the Earth's sister planet this night to see how it shines.

Top of Page

Lunar Almanac for April 2012

Phases of the Moon

Phase and Date(s)

Best viewed before local
midnight

New
21

Deep Space Objects

1st. Qtr
29

Planets & Moon

Full
06

Moon

Last
Qtr 13

Deep Space & Planets

Topic of the month: Leo, Spring Sky King

The constellation of Leo is usually agreed to resemble a lion, and is one of the few constellations that is regarded to appear like the animal it purports to display. The stars that make up the "head" of this stately lion, are often referred to as "the Sickle." This designation is not an actual constellation, but what is known as an asterism. Often sought by star gazers as a symbol of Spring approaching, the sickle is made up of six naked eye stars. The constellation is visible eight months of the year, and because of its station far from the bright stars of the Milky Way galaxy, it is possible to see many of the galaxies that are outside of our own.

The most prominent star in Leo is Regulus, also called Alpha Leonis and is the brightest star of the constellation. Regulus is less than a degree off ecliptic and nearly marks the location of the Summer sun in late August. Because of its proximity to the ecliptic, Regulus can often be seen near a bright planet, such as it will be this month when Mars passes near it. Be sure to watch the wandering of Mars through the constellation of Leo and the dance between it and Regulus. Regulus is a multiple star, consisting of three components, the largest being a young blue star, a second star that is 7.9 magnitude and another that is too faint to detect in a small scope.

Very close to Regulus, photographic plates revealed the Leo dwarf galaxy, a small nearby dwarf galaxy that is considered one of the Milky Way's satellite galaxies. This means that it is actually in orbit around our own galaxy, along with 11 other dwarf galaxies that have been identified.

This discussion of Leo would not be complete with mentioning some of the other well-known stars. Algeiba is part of the Sickle or lion's mane. It is a fine double star, although it takes a bit larger telescope to enjoy. It was discovered in 1782 by William Herschel. Denebola, a star of second magnitude whose name means "tail of the lion." The unnamed star, Eta, is one of the truly bright stars of the sky. It is a bright supergiant star, 2,000 light years away from Earth. This star is 13,000 times brighter than our own Sun. If it were as close as Regulus, it would be 6 times brighter than Sirius, the brightest star in the night sky. The upper star on the lion's hind quarter, called Zosma or Delta Leonis, is a very well-studied star, about 58 light years away.

Deep sky observers can seek out a number of bright nearby galaxies that are part of the Como-Virgo cluster that was featured last month on this page. (Click the previous month issue button to read more.) Charles Messier identified four of the brightest galaxies in this area of the sky, although he also overlooked a few. M65 and M66 are also known as the Leo triplet, because they are associated with NGC 3628. These galaxies are physically interacting with each other, not just associated by line of sight observations. The Messier pair 65/66 is about 9.3 magnitude, easily within the range of a small amateur telescope, but only at a dark site during a night when the Moon doesn't interfere. The galaxies of the M95/M96 pair are spiral galaxies, M95 with a conspicuous bar on deep sky images. Slightly above this pair, the galaxy NGC 3379 that is sometimes called M105 can be found, although it is not singled out on the chart below, it is in the general vicinity. These galaxies and their small companions are also gravitationally bound. One last favorite of mine that is located in Leo, but was not discovered by Charles Messier, is the galaxy NGC 2903 just off the last bright star of the lion's head. The visual brightness of this galaxy is 8.9 magnitude and it is also a barred spiral. It is known to contain a large number of young, bright globular clusters orbiting its galactic center and it seems to have a high rate of star formation activity.

Lastly, Leo is home to the radiant of one of the most famous meteor showers, the Leonids. This shower occurs annually around November 17, with a predicted rate of 10 meteors per hour. On certain occasions the shower has surprised us by producing fabulous shows, the last window for the productive shower being 1998-2002. Rates up to 500 per hour were recorded. The parent comet that causes this shower is called Tempel-Tuttle after the two astronomers who discovered it during its return in 1866.

To see what fabulous views can be captured of these distant galaxies, I offer these links to Astronomy Picture of the Day.

M 65 - Wow, it never looked like this my telescope! M 66 or click to see all three spiral galaxies of the Leo triplet. The "other" Leo triplet that includes M95 M96 and NGC 3379 and NGC 2903 These views are not typical of the small telescope view of the "faint fuzzies" instead they show us the beauty and structure of nearby spiral galaxies.

--See You Under the Stars!
Astra for Astra's Almanac

The star chart above was generated by Stellarium, a free open source planetarium program. The above image was created by Dawn Jenkins, using Stellarium and a graphic editing program to format the image for this web page. Editing was done for educational purposes only. Stellarium offers much more to amateur astronomers and is being used in planetariums and to guide telescopes in the field. Simple charts like the one above can be used on the internet for non-profit, illustration purposes. Proper credit is due of course! Thank you to the makers of this fine program from Astra's Star Gate.